Conventionally, copper is an important engineering metal since it is widely used in its unalloyed condition as well as in alloys with metals. In the unalloyed form, it has an extraordinary combination of properties which make it the basic material in the electrical industry, some of those properties being its high electrical and thermal conductivity and corrosion resistance. Because of its low strength of unalloyed copper, solute atoms introduced into solid solution in the solvent-atom lattice and invariably produces an alloy which is stronger than the pure metal. But the solute atoms have the maleficent effect of decreasing the electrical conductivity of pure copper with increasing the amount of the solute atoms. That is, the result of solute additions is to raise the strength and to decrease the eloectrical conductivity as a function of the amounts. Representative of copper alloys are C194 alloy and C195 alloy of Olin Company, USA, and PMC-102 alloy of Poongsan Corp., Korea, (C19010) (Korean Pat. Publication No. 84-1426, U.S. Pat. No. 4,466,939). Above alloys are well known as alloys exhibiting excellent mechanical properties, especially high tensile properties. Among the disadvantages of using these alloys are the low electrical conductivity (% IACS). Also, C194 and C195 were found to exhibit brittleness of corner crack when hot working since includes considerable amount of Fe, and difficulty in their cold-working process since high rolling ratio.
The uses of the lead-frame materials for surface mounting or power device depand mainly on the property of high electrical and thermal conductivity than high strength because of heat dissipation ability. The achievement of high strength without the much expense of electrical conductivity is obtained by precipitation hardening.
The precipitation hardening is produced by solution treating and quenching an alloy in which a second phase is in solid solution at the elevated temperature but precipitates upon quenching and aging at a lower temperature. In order to occur precipitation hardening, the second phase must be soluble at an elevated temperature but must exhibit decreasing solubility with decreasing temperature. Because of the finely dispersed second-phase particles, these alloys have high conductivity. Developed alloys geared to these needs are the alloy of Olin company, USA, (Cu-o0.5Cr-1.3Zr-0.05Fe, U.S. Pat. No. 4,224,006), KFC alloy of Kobe, Japan (Cu-0.1Fe-0.03P-X, where X is third element or misch-metal, Japanese Patent Publication No. SHO 58-53057), the alloy of Japan Mining Company (Cu-o0.13Fe-0.04P-0.32Zr, Japanese Patent Laid-Open No. SHO 62-214144) etc. But they have the disadvantages of high cost in alloying elements and not enough for conductivity (% IACS; below 85) and elongation. On the other hand, the alloy containing Nb is the alloy of Olin company, USA (Japanese Patent Laid-Open No. SHO 53-44422), but it also has the disadvantages of high cost in alloying elements and conductivity (% IACS) is in serious question.
It is therefore desirable to develop alloys which possess high conductivity and strength as well as low cost.